The present invention is broadly concerned with flingicidal compositions, and methods of use, which provide improved efficacy in controlling parasitic fungi in plants. More particularly, the compositions and methods of use of the invention include fungicidally effective amounts of both phosphate, preferably in the form of either mono, di, tri or dipotassium phosphate (KH.sub.2 PO.sub.4, K.sub.2 HPO.sub.4) and phosphonate, preferably in the form of either mono or dipotassium phosphonate (KH.sub.2 PO.sub.3, K.sub.2 HPO.sub.3), in aqueous solution.
According to another aspect of the present invention, the compositions and methods of use of the invention include growth response effective amounts of both phosphate, preferably in the form of either mono or dipotassium phosphate (KH.sub.2 PO.sub.4, K.sub.2 HPO.sub.4) and phosphonate, preferably in the form of either mono or dipotassium phosphonate (KH.sub.2 PO.sub.3, K.sub.2 HPO.sub.3), in aqueous solution.
Phosphorus is an essential major element in plant nutrition because it governs the energy producing reactions, including those that are oxidative, and photophosphorylative and the production of adenosine diphosphate (ADP) and adenosine triphosphate (ATP). Energy-rich phosphate bonds of ADP and ATP provide the energy for many of the physiological reactions that occur in plants.
The element phosphorous appears in two general forms that concern the present invention--phosphonate and phosphate. The term "phosphonate," sometimes also referred to as "phosphite," means the salts (organic or inorganic) of either phosphonic acid or phosphorous acid. Phosphonic and phosphorous acids have the formula H.sub.3 PO.sub.3 and a molecular weight of 82.00. Their structures from the International Union of Pure and Applied Chemistry are shown below: ##STR1##
The term "phosphate" means the salts (organic or inorganic) of phosphoric acid having the formula H.sub.3 PO.sub.4, molecular weight of 98, and has the following structure: ##STR2##
In the past, various phosphonate compounds have been proposed as useful in fungicidal and fertilizer compositions for application to plants. See, e.g., U.S. Pat. Nos. 4,075,324 and 4,119,724 to Thizy, describing phosphorous acid, its inorganic and organic salts, as a plant fungicide; U.S. Pat. No. 4,139,616 to Dueret, describing fungicidal compositions based on phosphorous acid esters and salts thereof; U.S. Pat. No. 4,542,023 to Lacroix et al., describing organophosphorus derivatives as possessing systemic and contact fungistatic and fungicidal activity; U.S. Pat. Nos. 4,698,334 and 4,806,445 and 5,169,646 to Horriere et al., describing fungicidal compositions based on alkyl phosphonates; U.S. Pat. Nos. 4,935,410 and 5,070,083 to Barlet, describing fungicidal aluminum tris-alkyl-phosphonate compositions; and U.S. Pat. No. 5,514,200 to Lovatt, describing formulations of phosphorous-containing acid fertilizer for plants. (The teachings of the proceeding U.S. Patents are hereby incorporated by reference.) The above references disclose phosphonate compositions have been found to be effective for protecting plants, and particularly grape vines, citrus and fruit trees and tropical plants, against fungal attack.
Once assimilated, phosphonates have been shown to enhance the phytoimmune system. The phosphonate induced stimulation of the phytoimmune system is triggered by the induction of ethylene production, followed by a rapid accumulation of phytoalexins at the site of infection. Phosphonates have also been shown to have detrimental effect on the growth of Phycomycetes. See, Pegg, K. G. and deBoer, R. F., "Proceedings of the Phosphonic (Phosphorous) Acid Work Shop, "Australiasian Plant Pathology, Vol. 19 (4) 1990.
In accordance with this development of the present invention, however, it has recently been discovered that phosphonates exacerbate the non-target Ascomycete fungi, and other fungi producing an eiphytotic outbreak of much greater magnitude than the infections occurring without phosphonate treatment. This phenomenon is known as pathological acerbation.
In the past, phosphates were not viewed as a solution to pathological acerbation of Ascomycete fungal infections. This is because phosphates are viewed primarily as a fertilizer with only limited, or even detrimental, fungical properties. For example, U.S. Pat. No. 5,514,200 teaches that phosphate fertilizers inhibit beneficial symbiosis between plant roots and mycorrhizal fungi, and further promote bacterial and fungical growth in the rhizosphere, including the growth of pathogenic fungi and other small soil-borne organisms. (Col. 2, lines 18-28). Phosphates have also been considered to be a competitive inhibitor for phosphonate assimilation, thus inhibiting the ability of phosphonates to protect against fungus attack. See, Pegg, K. G. and deBoer, R. F., "Proceedings of the Phosphonic (Phosphorous) Acid Work Shop, "Australiasian Plant Pathology, Vol. 19 (4), pp. 117 and 144, 1990. Yet further, phosphonates and phosphates were believed to be "biological strangers," with the presence of phosphonates or its esters, exerting little or no influence on enzyme reactions involving phosphates. Robertson, H. E. and Boyer, P. D., "The Biological Inactivity of Glucose 6--phosphonate, Inorganic Phosphites and Other Phosphites," Archives of Biochemistry and Biophysics, 62 pp. 380-395 (1956).
Accordingly, the requirements for a successful phosphonate-based fungicide depend on the elimination of the phosphonate-induced pathological ascerbation of Ascomycete fungical infections.
Moreover, the prior art teaching that phosphates and phosphonates are "biological strangers" is relevant to the lack of teaching of use of a composition of both for any agricultural use.